In a typical cellular radio system, wireless terminals, also known as mobile stations and/or user equipments (UEs), communicate via a radio access network (RAN) to one or more core networks. The radio access network covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a radio base station (RBS), which in some networks may also be called, for example, a “NodeB” (UMTS) or “eNodeB” (LTE). A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. Another identity identifying the cell uniquely in the whole mobile network is also broadcasted in the cell. The base stations communicate over the air interface operating on radio frequencies with the user equipment units (UE) within range of the base stations.
In some versions of the radio access network, several base stations are typically connected, e.g., by landlines or microwave, to a controller node, such as a radio network controller (RNC) or a base station controller (BSC), which supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the second generation (2G) Global System for Mobile Communications (GSM). The UMTS terrestrial radio access network (UTRAN) is essentially a radio access network using wideband code division multiple access for user equipment units (UEs). In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks and UTRAN specifically, and investigate enhanced data rate and radio capacity. Specifications for the Evolved Packet System (EPS) have completed within the 3rd Generation Partnership Project (3GPP) and this work continues in the coming 3GPP releases. The EPS comprises the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), also known as the Long Term Evolution (LTE) radio access, and the Evolved Packet Core (EPC), also known as System Architecture Evolution (SAE) core network. E-UTRAN/LTE is a variant of a 3GPP radio access technology wherein the radio base station nodes are directly connected to the EPC core network rather than to radio network controller (RNC) nodes. In general, in E-UTRAN/LTE the functions of a radio network controller (RNC) node are distributed between the radio base stations nodes, e.g., eNodeBs in LTE, and the core network. As such, the radio access network (RAN) of an EPS system has an essentially “flat” architecture comprising radio base station nodes without reporting to radio network controller (RNC) nodes.
3 GPP Long Term Evolution (LTE) uses orthogonal frequency division multiplexing (OFDM) in the downlink and Discrete Fourier Transform (DFT)-spread OFDM in the uplink. The basic LTE downlink physical resource may thus be seen as a time-frequency grid as generally illustrated in FIG. 1, where each resource element corresponds to one OFDM subcarrier during one OFDM symbol interval.
In the time domain, LTE downlink transmissions are organized into radio frames of 10 ms, each radio frame consisting of ten equally-sized sub-frames of length Tsub-frame=1 ms, as generally illustrated in FIG. 2.
Furthermore, the resource allocation in LTE is typically described in terms of resource blocks, where a resource block corresponds to one slot (0.5 ms) in the time domain and 12 contiguous subcarriers in the frequency domain. Resource blocks are numbered in the frequency domain, starting with 0 from one end of the system bandwidth.
Downlink transmissions are dynamically scheduled, e.g., in each sub-frame the base station transmits control information about to which user equipments data is transmitted and upon which resource blocks the data is transmitted, in the current downlink sub-frame. This control signalling is typically transmitted in the first 1, 2, 3 or 4 OFDM symbols in each sub-frame. A downlink system with 3 OFDM symbols as control is generally illustrated in FIG. 3.
LTE uses hybrid-Automatic Repeat Request (HARQ), where, after receiving downlink data in a sub-frame, the user equipment attempts to decode it and reports to the base station whether the decoding was successful (Acknowledge, ACK) or not (Not acknowledge, NACK). In case of an unsuccessful decoding attempt, the base station may retransmit the erroneous data.
Uplink control signalling from the user equipment to the base station generally comprises:
                hybrid-ARQ acknowledgements for received downlink data.        user equipment reports related to the downlink channel conditions, used as assistance for the downlink scheduling.        scheduling requests, indicating that a user equipment needs uplink resources for uplink data transmissions.        
If the user equipment has not been assigned an uplink resource for data transmission, the Layer1/Layer2 (L1/L2) control information, such as, channel-status reports, hybrid-ARQ acknowledgments, and scheduling requests, is transmitted in uplink resources, i.e. resource blocks, specifically assigned for uplink L1/L2 control on Rel-8 Physical Uplink Control CHannel (PUCCH). As illustrated in FIG. 4, these resources are located at the edges of the total available cell bandwidth. Each such resource consists of 12 “subcarriers”, that is, one resource block, within each of the two slots of an uplink sub-frame. In order to provide frequency diversity, these frequency resources are frequency hopping on the slot boundary, i.e. one “resource” consists of 12 subcarriers at the upper part of the spectrum within the first slot of a sub-frame and an equally sized resource at the lower part of the spectrum during the second slot of the sub-frame or vice versa. If more resources are needed for the uplink L1/L2 control signalling, e.g. in case of very large overall transmission bandwidth supporting a large number of users, additional resources blocks may be assigned next to the previously assigned resource blocks.
The reasons for locating the PUCCH resources at the edges of the overall available spectrum are two-fold:                Together with the frequency hopping described above, this maximizes the frequency diversity experienced by the control signalling.        Assigning uplink resources for the PUCCH at other positions within the spectrum, i.e. not at the edges, would have fragmented the uplink spectrum, making it impossible to assign very wide transmission bandwidths to single user equipment and still retain the single-carrier property of the uplink transmission.        
The bandwidth of one resource block during one sub-frame is too large for the control signalling needs of a single user equipment. Therefore, to efficiently exploit the resources set aside for control signalling, multiple user equipments may share the same resource block. This is done by assigning the different user equipments different orthogonal phase rotations of a cell-specific length-12 frequency-domain sequence and/or different orthogonal time-domain covers covering the sub-frames within a slot or sub-frame.
PUCCH Format 3
When carrier aggregation is used in LTE, one uplink carrier is designed to carry the HARQ-ACK/NACK bits for all DL carrier PDSCH transmissions. To enable the possibility to transmit more than four bits of A/N, PUCCH Format 3 may be used. The basis for Format 3 is DFT-precoded OFDM, see FIG. 5. The signalling to configure PUCCH Format 3 with transmit diversity and the corresponding ACK/NACK transmission is shown in FIG. 6.
If the number of ACK/NACK bits is up to 11, then the multiple ACK/NACK bits, which may also include scheduling request (SR) bits, are Reed-Müller (RM) encoded to form 48 coded bits. The coded bits are then scrambled with cell-specific sequences. 24 bits are transmitted within the first slot and the other 24 bits are transmitted within the second slot. The 24 bits per slot are converted into 12 quadrature phase shift keying (QPSK) symbols, spread across five DFT-spread (DFTS)-OFDM symbols using an orthogonal cover code, DFT precoded and transmitted within one resource blocks (bandwidth) and five DFTS-OFDM symbols (time). The spreading sequence is UE-specific and enables multiplexing of up to five users within the same resource blocks. For the reference signals, cyclic shifted CAZAC sequences, e.g. the computer optimized sequences, are used. To improve orthogonality among reference signals even further, an orthogonal cover code of length two may be applied to the reference signals. However, this is not used in LTE Rel.10.
If the number of ACK/NACK bits exceeds 11, then the bits are split into two parts and two RM encoders are used, one for each part respectively. This is known as the dual-RM code. Up to 20 ACK/NACK bits, plus one SR bit, may therefore be supported by PUCCH Format 3. Each encoder in the dual-RM code outputs 24 bits which are converted to 12 QPSK symbols per slot and the two sets of 12 QPSK symbols are interleaved over the subcarriers so that the first encoder maps (It shall be noted that in the “map to . . . ” operation a cell, slot and symbol specific cyclic shift of the symbols in time domain is included as to provide inter-cell interference randomization) its 12 symbols onto odd subcarriers and the second encoder onto even subcarriers, where 6 odd and 6 even sub-carriers are assumed per slot. The 12 QPSK symbols per slot are then spread across the five DFTS-OFDM symbols using one out of five orthogonal cover codes, as in the single-RM code case. Details of the encoding and multiplexing are shown in FIG. 7 and FIG. 8, respectively where in FIG. 8 the following algorithm is used in the Dual Codeword Combiner operation in which {tilde over (b)}0, {tilde over (b)}1, {tilde over (b)}2, . . . , {tilde over (b)}23 is the output sequence from the first encoder and {tilde over ({tilde over (b)}0, {tilde over ({tilde over (b)}1, {tilde over ({tilde over (b)}2, . . . , {tilde over ({tilde over (b)}23 the output sequence from the second encoder and NscRB=12, the number of subcarriers per resource block.
The output bit sequence b0, b1, b2, . . . , bB-1 where B=4·NscRB is obtained by the alternate concatenation of the bit sequences {tilde over (b)}0, {tilde over (b)}1, {tilde over (b)}2, . . . , {tilde over (b)}23 and {tilde over ({tilde over (b)}0, {tilde over ({tilde over (b)}1, {tilde over ({tilde over (b)}2, . . . , {tilde over (b)}23 as follows:
Set i, j = 0while i < 4 · NscRB   bi = {tilde over (b)}j,   bi+1 = {tilde over (b)}j+1   bi+2 =  ,   bi+3 =     i = i + 4,   j = j + 2,end whilePUCCH Format 3 Diversity with Space Time or Space Frequency Encoded Transmit Diversity
Using an Alamouti encoder to provide transmit diversity is well known and there are solutions on how to apply this to the PUCCH Format 3.
When combined with single-carrier frequency division multiple access (SC-FDMA), the well-known Alamouti scheme may be applied within a SC-FDMA symbol, on the six pairs of modulation symbols before the DFT operation, as depicted in FIG. 9 and also shown in FIG. 10.
The QPSK modulated symbol si and si+1 are Alamouti encoded together according to the Alamouti code to form a Space Time Block Code (STBC):
         (                                        s            i                                                s                          i              +              1                                                                        s                          i              +              1                        *                                                -                          s              i              *                                            )  
It is also possible to perform the Alamouti encoding on the DFT precoded symbols, before the IFFT in form of a space frequency block code (SFBC). However, then the single carrier property is lost and therefore has the modified SFBC been introduced. The Alamouti scheme may be modified as depicted in FIG. 12 in order to guarantee the same cubic metric (CM) as STBC on both transmit antennas, see FIG. 11. Cubic metric (CM) is a measurement on how much intermodulation distortion the signal produces when amplified in a non-ideal (non-linear) power amplifier.
In practice, the 12 sub-carriers are divided into two groups of 6 sub-carriers, and within each group the Alamouti scheme is applied on the first sub-carrier and the sixth sub-carrier, on the second sub-carrier and the fifth sub-carrier and on the third sub-carrier and the fourth sub-carrier. Here again, performance degradation due to channel frequency selectivity may arise as the frequency distance between symbols jointly encoded by the SFBC increases but this degradation will be limited thanks to the small bandwidth of PUCCH.
A problem with the above earlier disclosed procedures is coverage of the PUCCH Format 3 transmissions. A further problem is the increased detection complexity with joint detection of the two dual RM encoded codewords when transmit diversity is used, as illustrated at least in part by the Actions 1301-1308 in FIG. 13.
In Action 1301-1302, a set 1 of n1 number of information bits are encoded using a codeword 1, and a set 2 of n2 number of information bits are encoded using a codeword 2.
In Action 1303, the sequences may then be combined and interleaved, by alternating the symbols from the first and second decoder, as shown in FIG. 8.
In Action 1304, the sequences may be transmit pre-processed or transmit diversity encoded as shown in FIG. 10 and FIG. 11.
In Action 1305, the sequences may be transmit processed for antenna 1 and antenna 2, also shown in FIG. 10 and FIG. 11.
In Action 1306, a PUCCH Format 3 transmission to a network node may be performed.
In Action 1307, a network node may receive the PUCCH Format 3 transmission.
In Action 1308, the network node may perform a joint detection of the two encoded codewords 1 and 2 to obtain a detected joint sequence of set 1+set 2 comprising n1+n2 information bits.
This conventional transmit diversity joint RM codeword processing of the bit or symbol sequences in the network node detection will result in a detection complexity of 2n1+n2 number of hypotheses.